Vernier-tuned Sampled Grating Distributed Bragg Reflector (VTDBR) monolithic tunable lasers are now entering the production phase in telecommunications applications. These tunable lasers are unique in that they offer wide wavelength tuning (e.g., 1525 to 1565 nm) and fast wavelength tuning (e.g., full sweep in microseconds) all on the same monolithic chip. Such a tunable laser will be referred to herein as a Semiconductor Monolithic Tunable Laser Source (SMTLS). SMTLS have a characteristic sweep that is very short. However, the sweep may include potentially impactful non-linearities in the wavelength sweep. These non-linearities could be as short as 100 s of ns, or longer.
A typical measurement system begins measurement at the beginning of a wavelength sweep by the SMTLS, and uses the sweep rate to determine the wavelength at subsequent times during the sweep using the formulaWLa=WLstart+timea*sweep rate
For this formula to be accurate, the sweep must be linear with time.
Alternatively, a swept wavelength meter can be used to determine the wavelength at each point during the sweep. An exemplary wavelength meter may be a model 410 Wavelength Meter manufactured by dBm Optics.
There are two effects from short-period non-linearities. First, the measurements made during the period of non-linearity are not representative of the actual results at those predicted wavelengths. Second, the potentially large amplitude variations that can occur during these non-linearities in wavelength (due to relatively high change in loss versus wavelength of a measured device in the vicinity of the non-linearity) can cause the measurements immediately following the non-linearity to be incorrect, due to explicit or implicit filtering of the signal. For example, the signal may jump to a much larger signal during a non-linearity, and even after the non-linearity, the signal may not have settled back to the nominal level due to filter settling time.